Ancient Galaxy Is Most Distant Ever Found

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Astronomers have spotted the farthest-flung galaxy in the known
universe.

The newfound galaxy, known as EGSY8p7, lies about 13.2 billion
light-years from Earth — meaning astronomers are now seeing the
mass of stars as it existed just 600 million years or so after
the
Big Bang that created the universe.

The discovery team used an infrared spectrograph at the Keck
Observatory in Hawaii to detect EGSY8p7's "Lyman-alpha emission
line" — basically, hydrogen gas heated up by ultraviolet
radiation streaming from the galaxy's newborn stars.

Seeing a Lyman-alpha line at such a great distance came as a
surprise to the researchers.

"We frequently see the Lyman-alpha emission line of hydrogen in
nearby objects, as it is one of the most reliable tracers of star
formation," study lead author Adi Zitrin, of the California
Institute of Technology in Pasadena,
said in a statement. "However, as we penetrate deeper into
the universe, and hence back to earlier times, the space between
galaxies contains an increasing number of dark clouds of
hydrogen, which absorb this signal."

The unexpected result could shed new light on how
the universe evolved in its youth, researchers said.

For example, astronomers think the universe was completely opaque
to Lyman-alpha emission for about 400 million years after the Big
Bang, thanks to that pervasive hydrogen. But things then began
changing, as the first galaxies formed; radiation from their
stars started splitting the hydrogen into its constituent protons
and electrons.

This process, known as "cosmic reionization," probably proceeded
gradually, with hydrogen being burned off in numerous localized
but ever-expanding bubbles, researchers said. These bubbles
eventually met and overlapped, making the universe transparent to
Lyman-alpha light.

The detection of EGSY8p7's Lyman-alpha emission suggests that the
reionization process was far from uniform, with some patches of
space cleared of hydrogen much faster than others (perhaps
because the newborn stars in such regions were exceptionally
powerful), researchers said.

"In some respects, the period of cosmic reionization is the final
missing piece in our overall understanding of the evolution of
the universe," Zitrin said. "In addition to pushing back the
frontier to a time when the universe was only 600 million years
old, what is exciting about the present discovery is that the
study of sources such as EGSY8p7 will offer new insight
into how this process occurred."

The study announcing EGSY8p7's detection will be published soon
in the Astrophysical Journal Letters.